1. Field of the Invention
This invention relates to a magnetic head carriage, so called a head arm member or an access arm, for a hard disc drive formed by drawing or extrusion molding, more particularly to a carriage, the head arm member or access arm, with novel surface finish polish.
2. Description of Related Art
FIG. 1 is a perspective view of a magnetic head carriage as a head arm member or an access arm for a hard disc drive, hereinafter HDD is used, as an example. The carriage 1 includes a base member 1a and a plurality of plate members 1b as arm members formed integrally as a comb shape extending parallel in the outer direction from the base member 1a. A plurality of slits 1f are provided between the plate members 1b. A support shaft hole 1c is provided in the base member 1a, and an opening 1e for lessening the weight of the plate members 1b and a head installation hole 1d for installing the magnetic head are formed by cutting work on the top of each plate member 1b formed in the triangle shape or the like viewed from the upper direction. A plurality of head arm members 1b move between a plurality of discs in the protrudent direction, and the magnetic head installed in the top position is capable of reading information from the disc.
Here, one example, in which the shape of the carriage is different from the above described type, of the head arm portion of the magnetic disc is explained using FIGS. 2A, 2B and 3.
In the disc apparatus, a magnetic head is provided on the both sides or a single side of each magnetic disc in a plurality of magnetic discs. The magnetic head is installed in the pointed end of a suspension, and the suspension is installed in the top position of a carriage arm of an actuator assembly. Thus, the carriage arm, namely the magnetic head, is capable of being positioned in an appointed position by moving in the radius direction of the magnetic disc when the actuator of the actuator assembly is driven.
FIG. 3 is a perspective view of one example of the actuator assembly. In the actuator assembly 6 shown in FIG. 3, one side of a rotating shaft 5 is a driving portion 7 as the actuator and the other side is a carriage arm 8 rotating by the rotating shaft 5. The driving portion 7 includes a voice coil 9 installed on a coil supporting plate 7a and a flexible printed circuit (FPC) 7c supported by a fixed portion 7b. Here, the numeral 7d means a pressure plate. The necessary numbers of carriage arms are provided corresponding to the numbers of the magnetic discs, and a magnetic head assembly 11 is installed in two sides or one side of the top installation portion 10 as shown in FIGS. 2A and 2B, thus the magnetic head 13 is capable of being positioned in the appointed position in the radius direction of the magnetic disc 4. In the top installation portion 10, a hole 10a is provided for installing the magnetic head assembly 11 on two sides or one side of the top installation portion 10. Here, a magnetic arm means a block in which the magnetic head assembly 11 is installed in the actuator assembly 6.
This invention relates to the magnetic head carriage described above made of improved materials. Usually, in the above described carriage, the opening 1e or the hole 1d is formed by cutting work materials after drawing or extrusion molding. In FIG. 1, a bur would be made around each plate portion 1b of above mentioned magnetic head carriage or in angle positions of holes 1c and 1d, and opening 1e, by cutting work, drawing, or extrusion molding. If the apparatus is assembled without treating the bur, there are problems in which the bur damages the disc surface by contacting with the disc surface and the disc and the head would be damaged because the bur would be caught between the disc and the head and cutting work scraps would drop on the disk. Thus, it should be carefully done to remove the bur and chamfer. Further, a film or an alien substance would adhere to the plate members 1b in the hard disc assembly process for the next process, thus it should be securely done to remove and clean the film and alien substance. For the hard disc drive, the disc rotates at a high speed and the gap between the magnetic head and the magnetic disc is 0.005 to 0.10 .mu.m as an ultra-minute mechanism, thus such high precision rate that thickness dimensional tolerance of each plate member 1b and form tolerance for each plate should be under 20 .mu.m is required to the above described carriage. The above described precision is so high that HDD will crush even if tiny dust exists in the gap between the magnetic disc and the magnetic head when the disc is running because the magnetic head and the magnetic disc are damaged and the chip would damage the magnetic head and the magnetic disc as a synergy effect.
In the head arm member 1 of the above described FIG. 1, however, it is impossible to automatically remove the bur made in the angle position of the hole 1c, 1d, and 1e of the plate member 1b with comb shape because a processing tool is not able to enter inside. Thus, many people cannot help cleaning the bur using a brush, then actually a large amount of money is spent for just only finishing process. Further, in the method of removing the bur by a human being's hand, it might be impossible to make processing for the inside of the above described head arm member 1 arranged in a complicated manner. Thus, there is a problem in which the head arm member 1 is not capable of being small and light because the structure of the head arm member 1 should be changed to the simpler structure. Further, this type of problem is found not only in the above described head arm member 1, but also in surface processing or surface treatment for precision parts having the hole or the opening inside and the narrow wide slit outside, thus there is another problem in which the capability of producing a variety of products is disturbed.
Further, there are electrolytic polishing, a shot method, or an ultrasonic method as a polishing method for those portions. There are defective points in which dimensional tolerance of each plate member is not capable of being solved if the bur is removed enough by electrolytic polishing and inside processing is impossible although outside surface processing is possible by the shot method. Further, the ultrasonic method does not have enough power to remove the bur, thus processing becomes uneven. Thus, those processing methods are not capable of being used because the surface shape inside the comb teeth made with a micron accuracy is destroyed. Unavoidably, those portions are processed by a brush by the human being's hand using abrasive material. Thus, there have been defective points in which polish efficiency has been very bad and the cost would be high because one hundred percent test has been required since the polish processing has been made by the human being's hand. Further, the bad quality rate based on processing has been high.
The applicant discloses a method and an apparatus in which the bur of the surface beyond one's reach or inside nonmagnetic parts is removed using a machine using magnetic beam processing additionally, so called magnetic polishing.
Here, surface finishing polish for the above described carriage based on the conventional manual processing is explained in detail. Conventionally, firstly, the big bur which can be seen by one's eye is removed roughly by rotating a metal brush as shown in FIGS. 4A, 4B, and 4C. The above described metal brush has the structure in which a number of wire brushes grow densely in a prop 14 in the same circle direction as shown in FIGS. 4A, 4B, and 4C, and, as shown in FIG. 4A, polish processing is made in such a way that the prop is rotated in the arrow direction and then the above described carriage is pressed by one's hand from one side. After the above described rough polish processing is finished, then small burs are removed by cutting with a knife using a microscope. In FIGS. 5 and 6, the picture of the carriage surface finished by the manual processing is shown. Here, FIG. 5 is a magnified picture of the portion of "A" of FIG. 7, and the magnification rate becomes bigger from the top to the bottom. Further, FIG. 16 is a magnified picture of the portion of "B" of FIG. 7, and the magnification rate becomes bigger from the top to the bottom.
As identified by the pictures clearly, one direction traces are kept in the carriage surface finished by manual processing. This phenomenon, as shown in FIGS. 4A, 4B, and 4C, is based on processing in which the only conspicuous bur is cut with the knife using the microscope by one's hand after rough removal is made by the metal brush with manual processing. Accordingly, the most part of the surface is kept with the rough removal condition, namely final polish condition in which polish processing was made by the metal brush.
Accordingly, as shown in the pictures of FIGS. 5 and 6, there are cutting stripe traces made mostly by the first rotating brush and kept on the finish surface. Further, face precision at least in the cutting portion would be dynamically beyond the range of a standard, 20 .mu.m comb thickness, because cutting volume depends on one's pressure since small burs are cut by one's hand with the knife. Further, manual processing requires skill, does not keep uniform processing, and increases costs because processing efficiency goes down if excellent finish is required. Recently, as the production method for the magnetic head carriage of the above described HDD, there is a tendency in which the carriage is assembled using each plate produced by a press working. This is based on the bur problem found in integral production. The HDD rotates at high speed, the magnetic head employs a surface method, and a space between the head and the disc is 0.05 to 0.10 .mu.m during disc s rotating, thus the head is so delicate as for surface stability to become unstable even if dust in the air enters in the space. Further, after the head collides with the disc once, the situation caused by dust and a broken piece produced by collision between both of them becomes suddenly bad. As a result, crushing occurs. Thus, metal chips should not exist there.
There is a risk, in which a small metal chip drops inside the HDD by HDD vibration, for surface finish by manual processing. For one thing, although a tiny bur can be removed by the knife as explained before, scratch stripe traces by the metal brush are kept on most of surfaces and the small burs exist on the edge of the scratch stripe traces. Secondly, the tiny burs are removed by cutting work with the knife, so there exist still more tiny burs on the edge in which the burs are removed by the knife. Still, an oversight occurs since visual observation is applied. Final finish by manual processing not only increases costs since manual processing is a time consuming job, but also occurs the above described defect points on the finish surface.
FIGS. 8 and 9 are pictures showing surface conditions by electrolytic polishing for reference. FIGS. 8 and 9 are magnified pictures of "A" and "B" of FIG. 7 in the same way as FIGS. 5 and 6. Here, referring to electrolytic polishing, the surface is smooth like a mirror according to electrolytic polishing, so the tiny bur exists little on the surface since electrolytic polishing is capable of polishing more powerfully than magnetic polishing of the present invention or the conventional manual processing. The biggest defect point of electrolytic polishing, however, is the impossibility for the polish extent not to be capable of being controlled. Generally speaking, the burs do not exist in the same way, but the size of the burs differ in various ways. The surface precision deteriorates since the tiny burs are removed excessively if electrolytic polishing is applied for a long time in order to remove big burs. Electrolytic polishing is capable of polishing notched surfaces better than the smooth surfaces, so the polish volume is not the same for all surfaces. Thus, the surface precision in which the plate thickness is within 20 .mu.m cannot be kept since over-cutting work occurs if all the burs are removed, and still the precision standard cannot be satisfied since the big burs are kept if the surface precision is tried to bucket. After all, electrolytic polishing cannot be used for finish polish of the above described carriage. Further, electrolytic polishing may be used only for the final finish polish, but this usage will increase processing steps and costs because polish processing is duplicated with other polish methods.